Get People's Permission

Always make sure your recipients want to receive an email message from you. For example, don't just send an email to all business cards collected at a trade show. Have your marketing team ask the person if it's okay to send them some email communications when they are collecting the person's business card. If they give you their permission, take note of it and add them to the list.
Have sales make invitations to a mailing list part of their job. Lead Liaison provides the ability for sales people to drop a contact into a lead nurturing cycle in a few clicks. If the contact provides their permission to send future touch points or have communication then you're in the clear.